1. Field of the Invention
The present invention relates to a robot arm mechanism having arms contracted and extended, and more particularly to a robot arm mechanism incorporating an arm driving mechanism for driving the arms to assume its contracted and extended positions.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of conventional robot arm mechanisms available in the process of producing semiconductors in which the robot arm mechanism is operated to have arms contracted and extended to handle works, i.e., objects to be treated. These objects may include works such as, for example, wafers and other precision parts that are to be transferred and then unloaded onto a work table by the robot arm mechanism.
One typical example of the conventional robot arm mechanism of this type is disclosed in, for example, Japanese Patent Laid-Open Publication No. 2000-208588. Such conventional robot arm mechanism 900 is shown in FIG. 20 as comprising a first arm link mechanism 910, a second arm link mechanism 920, a robot arm driving mechanism 930, and a link retaining mechanism 940.
The first arm link mechanism 910 consists of a quadric crank chain comprising a first arm link 911, a second arm link 912 substantially in parallel relationship with the first arm link 911, a third arm link 913, and a fourth arm link 914 substantially in parallel relationship with the third arm link 913. The second arm link mechanism 920 consists of a quadric crank chain comprising a first arm link 921, a second arm link 922 substantially in parallel relationship with the first arm link 921, a third arm link 923, and a fourth arm link 924 substantially in parallel relationship with the third arm link 923.
The first and second arm links 921, 922 of the second arm link mechanism 920 are substantially equal in length to the first and second arm links 911, 912 of the first arm link mechanism 910, respectively. The third arm link 923 of the second arm link mechanism 920 is integrally formed with and fixedly connected with the third arm link 913 of the first arm link mechanism 910.
The conventional robot arm mechanism 900 has a reference line 900a, and further comprises a robot arm driving mechanism 930. The robot arm driving mechanism 930 is adapted to drive the first arm link mechanism 910 so as to rotate the first arm link 911 and the second arm link 912 of the first arm link mechanism 910 with respect to the reference line 900a. 
The link retaining mechanism 940 consists of first and second joint cross linkages. The first joint cross linkage consists of a quadric crank chain comprising a first short link 941, a second short link 942 substantially equal in length to the first short link 941, a second long link 943, and a first long link 944 substantially equal in length to the second long link 943, wherein the first long link 944 of the first joint cross linkage of the link retaining mechanism 940 is crossed with the second long link 943 of the first joint cross linkage of the link retaining mechanism 940. The second joint cross linkage consists of a quadric crank chain comprising a first short link 945, a second short link 946 substantially equal in length to the first short link 945, a second long link 947, and a first long link 948 substantially equal in length to the second long link 947, wherein the first long link 948 of the second joint cross linkage of the link retaining mechanism 940 is crossed with the second long link 947 of the second joint cross linkage of the link retaining mechanism 940. Furthermore, the first short link 941 of the first joint cross linkage of the link retaining mechanism 940 is integrally formed with and fixedly connected with the first arm link 921 of the second arm link mechanism 920, and the second long link 947 of the second joint cross linkage of the link retaining mechanism 940 is integrally formed with and fixedly connected with the first arm link 911 of the first arm link mechanism 910.
The second long link 943 of the first joint cross linkage of the link retaining mechanism 940 is integrally formed with and fixedly connected with the third arm link 913 of the first arm link mechanism 910, and the first short link 945 of the second joint cross linkage of the link retaining mechanism 940 substantially equal in length to the second long link 943 of the first joint cross linkage of the link retaining mechanism 940, and integrally formed with and fixedly connected with the third arm link 923 of the second arm link mechanism 920. The second short link 942 of the first joint cross linkage of the link retaining mechanism 940 integrally formed with and fixedly connected with the first long link 948 of the second joint cross linkage of the link retaining mechanism 940.
The link retaining mechanism 940 thus constructed is adapted to pivotably retain the first arm link mechanism 910 and the second arm link mechanism 920 and keep a first angle θ901 substantially equal to a second angle θ902, wherein the first angle θ901 is an angle formed by the first arm link 911 of the first arm link mechanism 910 with the reference line 900a, and the second angle θ902 is an angle formed by the first arm link 921 of the second arm link mechanism 920 with the reference line 900a. 
The conventional robot arm mechanism 900 further comprises a robot arm member 951 having first and second end portions, and a handling member 952 for supporting and handling an object. The first end portion of the robot arm member 951 is integrally formed with and fixedly connected with the fourth arm link 924 of the second arm link mechanism 920. The handling member 952 is connected with the second end portion of the robot arm member 951.
The conventional robot arm mechanism 900 thus constructed makes it possible for the first arm link mechanism 910 and the second arm link mechanism 920 to be contracted and extended to assume its contracted and extended positions.
The conventional robot arm mechanism 900 thus constructed, however, encounters drawbacks resulting from the fact that the quadric crank chains constituting the first arm link mechanism 910, the quadric crank chain constituting the second arm link mechanism 920, and the quadric crank chain constituting the link retaining mechanism 940 may be easily flattened out, and accordingly vulnerable to deformation while the first arm link mechanism 910 and the second arm link mechanism 920 are extended to assume its extended position as shown in FIG. 20.
This means that the conventional robot arm mechanism 900 encounters a problem that the quadric crank chains constituting the first arm link mechanism 910, the quadric crank chain of the second arm link mechanism 920, and the link retaining mechanism 940 may be deformed due to, for example, a temperature change while the first arm link mechanism 910 and the second arm link mechanism 920 are extended, thereby making it difficult for the conventional robot arm mechanism 900 to accurately position the handling member 952 while the first arm link mechanism 910 and the second arm link mechanism 920 are extended, and accordingly aggravating the operating accuracy of the conventional robot arm mechanism 900.
The conventional robot arm mechanism 900 encounters another problem that the quadric crank chains constituting the first arm link mechanism 910, the quadric crank chain of the second arm link mechanism 920, and the link retaining mechanism 940 may be deformed due to, for example, an external force exerted thereon while the first arm link mechanism 910 and the second arm link mechanism 920 are extended, thereby making it difficult for the conventional robot arm mechanism 900 to accurately position the handling member 952 independently of the external force exerted thereon while the first arm link mechanism 910 and the second arm link mechanism 920 are extended, and accordingly aggravating the operating accuracy of the conventional robot arm mechanism 900.
The present invention is made with a view to overcoming the previously mentioned problems inherent to the conventional robot arm mechanism.